The present invention relates to keypads and molding techniques and more particularly, relates to a thin film keypad and method of making the thin film keypad.
Electronic devices, such as wireless telephones, have drastically reduced in size. These devices include keypads that must also be reduced in size. In particular, the manufacturers of these electronic devices have demanded that the keypads be extremely thin. Attempts at reducing the size and thickness of these keypads have met with various difficulties.
According to one method of constructing thin keypads, the keys are adhered to a plastic film. However, the keys often would not adhere adequately, especially if the keys and film are made of different materials (e.g., keys made of ABS and film made of polycarbonate or polyester).
Another method of making keypads is the insert mold design (IMD) technique. According to this technique, a cavity is formed in the film and the key is molded into the cavity. As a result, however, the film is on the outside of the keypad and graphics are printed on the film. One disadvantage of keypads made using the IMD technique is the limited extent to which the film can be stretched while retaining graphic quality. The dimensions of the keys (i.e., the height) made using the IMD technique are also limited.
Accordingly, there is a need for a thin film keypad where the keys will remain secured to a top surface of the thin film, even when materials are used that do not adhere together well.
In accordance with the needs addressed above, the present invention provides a thin film keypad and method of making same. According to one aspect of the present invention, the thin film keypad comprises a retainer sheet made of a thin film material and having a top and bottom surface. The retainer sheet includes at least one hole extending through the thin film material and at least one retainer anchor portion formed from a portion of the thin film material extending upwardly from the top surface. At least one keycap is molded onto a top surface of the retainer sheet and around the retainer anchor portion. The keycap includes a keycap anchor portion molded through the hole in the thin film material such that the keycap anchor portion and the retainer anchor portion mechanically secure the keycap to the retainer sheet.
According to another aspect of the present invention, the thin film keypad comprises a retainer sheet made of a thin film material and having a top and bottom surface. The retainer sheet includes a plurality of keycap attachment regions. Keycaps are molded onto a top surface of the retainer sheet at respective keycap attachment regions. The keycaps are molded around portions of the thin film material such that the keycaps are mechanically secured to the retainer sheet.
According to one embodiment, the thin film material is preferably a plastic material, such as polycarbonate or polyester, having a thickness in a range of about 0.005 in. (0.127 mm) to 0.010 in. (0.254 mm). The keycap is preferably made of a plastic material, such as polycarbonate, polycarbonate/ABS blend, or ABS.
One embodiment of the retainer sheet includes holes extending through the thin film material at the keycap attachment regions. The portions of the thin film material around which the keycaps are molded include edges of the thin film material around the holes. The portions of the thin film material around which the keycaps are molded also include flaps cut out from the thin film material and extending upwardly from the top surface.
According to further aspect of the present invention, a method of making a thin film keypad comprises forming at least one keycap attachment region on a thin film material with each keycap attachment region including at least one molding material passage region. The thin film material is placed into a molding tool having at least one keycap mold cavity such that each molding material passage region is located within each keycap mold cavity, respectively. A molding material is injected through the molding material passage region in the thin film material and into the keycap mold cavity such that at least one keycap is molded onto a top surface of the thin film material. The molding material flows around a portion of the thin film material such that the keycap is mechanically secured to the thin film material. The outline of the retainer sheet can then be cut from the thin film material such that the keys are molded onto the retainer sheet.
In one preferred method, forming each keycap attachment region includes forming at least one hole through the thin film material. The retainer sheet is placed in the molding tool with the hole positioned between the keycap mold cavity and an anchor mold cavity such that the molding material flows through each hole and around an edge of the thin film material. Forming the keycap attachment region also preferably includes cutting at least one flap from the thin film material to form the material passage region. The molding tool preferably includes a gate for injecting the molding material. Inserting the retainer sheet into the molding tool preferably includes inserting the gate through the material passage region such that the gate moves the flap into the keycap mold cavity. The molding material flows around each flap.
According to a further aspect of the present invention, a method of making a thin film keypad comprises forming a plurality of keycap attachment regions on a thin film material such that each keycap attachment region includes at least one hole and at least one material passage region. The thin film material is placed into a molding tool including a female side having keycap mold cavities and a male side having anchor mold cavities. The retainer sheet is positioned such that the holes are located between respective keycap mold cavities and anchor mold cavities and such that the material passage regions are located within respective keycap mold cavities. A molding material is injected through the material passage regions in the thin film material and into the keycap mold cavities. The molding material flows through the holes and into the anchor mold cavities such that keycaps are molded onto a top surface of the thin film material and are mechanically secured to the thin film material.
According to one method, forming the material passage regions includes cutting flaps from the thin film material. According to another method, forming the material passage regions includes forming formed hole portions from the thin film material.